Technical Field
The embodiments herein relate to a polylactic acid resin composition and a resin molded article thereof.
Description of the Related Art
While depletion of petroleum resources, a CO2 reduction, and the like have been perceived as problems, a polylactic acid using lactic acid obtained by fermenting a grain resource such as corn as a raw material has been attracting attention. Polylactic acid is a resin derived from a plant as described above and has the following characteristics: Polylactic acid has high rigidity, and is excellent in transparency. However, its applications have been generally limited as compared to an ordinary resin because of, for example, the following reasons: Polylactic acid generally has low heat resistance and low impact resistance, and hence typically cannot be used under a high-temperature condition.
Available as a method of improving the heat resistance of the polylactic acid is, for example, a method involving increasing its crystallinity through a heat treatment (annealing treatment). However, the method is generally not practical because of an extremely long heat treatment time.
In view of the foregoing, blending of various plasticizers and crystal nucleating agents into a resin composition using the polylactic acid as a polymer has been investigated as a method of solving those problems in recent years.
For example, the following has been proposed as an example of the blending (International Publication No. WO2008/010318A). A fatty acid ester formed of a dehydration condensate of a sugar alcohol and a fatty acid is used as the plasticizer, and a layered silicate is used as the crystal nucleating agent.
In addition to the foregoing, for example, the following has been proposed (Japanese Patent Application Laid-open No, 2007-130895 and Japanese Patent Application Laid-open No. 2011-208042). A glycerin fatty acid ester, an ester of succinic acid and triethylene glycol monomethyl ether, or the like is used as the plasticizer, and a fatty acid amide is used as the crystal nucleating agent.
However, generally applications where the resin composition disclosed in International Publication No. WO2008/010318A can be used are extremely limited owing to its low heat resistance. Moreover, the resin composition involves a problem in that productivity at the time of its mold forming is poor because a molded article thereof is liable to deform upon its removal from the mold unless a molding time during the mold forming is set to be long.
On the other hand, the impact resistance of the resin composition disclosed in each of Japanese Patent Application Laid-open No, 2007-130895 and Japanese Patent Application Laid-open No. 2011-208042 has been somewhat improved. However, a molded article excellent in impact resistance and migration resistance typically cannot be obtained from the resin composition because the resin composition is liable to be migrated in water or an alcohol. Further, the resin composition still has room for improvement because its productivity at the time of the mold forming thereof is typically not sufficient.
Accordingly, it would be desirable to provide a polylactic acid resin composition excellent in impact resistance, migration resistance, and heat resistance, and excellent in productivity at the time of the mold forming thereof, and a resin molded article thereof.